Is your internet slow? If your internet is Dial up then when calls are made, You are lagged.
Else
If other's are using the internet for videos, Games and well... GAMES then that may cause your game to generically lag after every byte transferred through your internet.
[My building kit ]: http://www.roblox.com/Thumbs-Up-cooldude999921s-Building-Kit-V6-item?id=130222938
Well if you do Web development, You study how the HTTPService is called by MPbs, Also known as
Mega Bits per second, Every bit has data and if that data is being used, The game connected to the Site, The Service, The Proxy will not respond as much, So when the game begins to run bytes, Those bytes/ Bits hardly run at all
[My building kit ]: http://www.roblox.com/Thumbs-Up-cooldude999921s-Building-Kit-V6-item?id=130222938